Your immune cells, barriers, and signaling molecules are all highly dependent on good nutrition.

But it's time to begin thinking beyond blueberries, vegetables, and chicken broth, and instead to begin delving into more advanced, little-known foods that can support your immune system with great efficacy.

These foods may sound scary, and some of them may be stinky, but they can give your immune system a huge boost that keeps disease, infection, and sickness from taking you down.

Of all the physical barriers between your internal organs and the outside world, your gastrointestinal tract is of primary importance when it comes to your immune system.

The gastrointestinal tract is like an internal skin, but it has about 150 times more surface than your outside skin does. It also contains the largest number of immune cells of your whole body—approximately 60 percent of your entire immune system!

Your gastrointestinal tract comes into contact with the largest amount and number of different molecules and organisms of any organ in your whole body, which makes sense when you consider that the average person ingests more than 25 tons of food over his or her lifetime.

1. Raw milk

Unpasteurized, grass-fed organic raw milk contains a host of beneficial bacteria that prime your immune system. Though not approved yet by the FDA, this type of milk is an outstanding source of nutrients, especially vitamin A, zinc, and digestive enzymes.

Raw milk also contains beneficial fats that will help your immune system.

Raw milk is a food that feeds and repairs your entire gastrointestinal tract. Although raw milk availability is limited in the United States depending on where you live, you can locate the source closest to you at RealMilk.com, and many natural grocery stores carry raw, unpasteurized milk from local farms.

2. Natto

If you're serious about boosting your immunity, then you must also add fermented foods, which are rich in bacteria that nourish your digestive tract.

Good bacteria have an extremely beneficial effect on your gut's immune system, your first line of defense against pathogens, and these foods also aid in the production of antibodies.

One of the most healthful but lesser-known fermented foods is natto. It's a slimy, scary-looking fermented soybean derivative that is an ancient cultured, enzyme-rich food full of friendly microorganisms that balance your inner ecosystem and help you to absorb Vitamin D (an incredibly important vitamin for your immune system).

I discovered natto while racing triathlons in Japan, and my preferred ingestion method is to wrap natto up inside a seaweed nori wrap, just like a burrito or a sushi hand-roll, with a little bit of white rice, yellow mustard, and fish.

3. Organ meats

Organ meats such as liver, kidney, heart, and other "scary" areas of an animal are very high in vitamins A and E, omega-3 fatty acids, beta-carotene, zinc, and conjugated linoleic acid (CLA), all of which provide your immune system with tons of concentrated support.

When it comes to organ meats, always choose organic and grass-fed.

Can't stand the taste of organ meats? You'd be surprised at how easy they are to prepare. For example, you can soak liver in raw milk or lemon juice overnight to remove any "gamy" flavor, dredge it in a couple of whisked eggs, and drag it through coconut or almond flour, then sauté in olive or avocado oil, and serve with red onions (another good immune-system booster chock-full of quercetin), mushrooms, and bacon. Bon appetit!

4. Coconut manna

Coconut oil is rich in lauric acid, which converts in your body to monolaurin. Monolaurin is the actual compound found in breast milk that strengthens a baby's immunity, and lauric acid can enhance adult immunity, too. This medium-chain fatty acid (MCFA) in coconut oil actually disrupts the lipid membranes of offending organisms and bacteria.

When selecting coconuts and coconut oil products, make sure you choose organic versions that are unrefined, unbleached, made without heat processing or chemicals, and are non-GMO.

One of my favorite little-known ways to consume coconut products is with the incredibly tasty "coconut manna," which is a mix of coconut meat and coconut oil that contains an incredible, flavorful, buttery profile perfect for spreading on crackers or eating by the spoonful.

5. Dirty vegetables

When it comes to fighting off pathogens, you simply can't do any better than eating an enormous variety of fresh, organic vegetables for the vitamins, minerals, antioxidants, and enzymes they contain.

However, when I'm eating vegetables—especially if they're from an organic source—I actually eat them "dirty," picked fresh from the garden or the produce aisle, so that I can get all the beneficial soil-based probiotics that tend to accumulate on the surface of organic vegetables (and fruits).

Don't be afraid of dirt! The good bacteria supports your immune system, and as long as you're eating organic, you don't need to worry about pesticides and herbicides.

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6. Mushrooms

Mushrooms strengthen your immune system because they are rich in protein, fiber, vitamin C, B vitamins, calcium, and other minerals.

Mushrooms also contain powerful compounds called beta-glucans, which are well-known for their immune-enhancing properties. The beta-glucans in medicinal mushrooms (especially reishi, shiitake, and maitake versions) are particularly notable for their ability to activate and modulate your immune system cells.

Beta-glucan also enhances immunity through a variety of other mechanisms, many of which are similar to those of the popular immune-boosting herbs echinacea and astragalus root. For example, beta-glucans bind to macrophages and other scavenger white blood cells of your immune system, thus activating their anti-infection activities.

7. Algae

Take one version of algae, for example: chlorella.

As foods go, chlorella is nearly perfect. It is a single-cell freshwater algae that acts as an extremely efficient detoxification agent by binding to toxins, such as mercury and other heavy metals and infectious agents, and then carries those out of your system.

The chlorophyll in chlorella also helps you process more oxygen, cleanses your blood, and promotes growth and repair of your tissues. You can find chlorella in powder and chewable form, and it can be used in smoothies and shakes, sprinkled on salads or soups, or simply eaten as is.

If you visit my website and do a search for "algae," you'll find a host of articles and podcasts I've produced about this amazing, slimy green superfood.

8. Garlic

Stinky garlic is incredibly beneficial to your immune system because it produces a trifold effect: It's antibacterial, antiviral, and antifungal.

I'm a firm believer that for ideal immune-system strength, you should be eating garlic nearly every day. One of the best things about garlic is that, unlike synthetic antibiotics, bacteria, viruses, and yeast build up no resistance to it.

For optimal immune-system boosting benefits, garlic should be eaten fresh, since the active ingredient of garlic (allicin) is destroyed within one hour of smashing the garlic cloves.

In other words, garlic capsules in supplement form are typically useless compared to, say, fresh roasted garlic that you've drenched in olive oil and sea salt and baked in the oven for a half hour.

In addition, the allicin in garlic is a natural chemical that is anti-carcinogenic, has been shown to lower LDL, lower total cholesterol, lower blood pressure, reduce your risk of blood clots and stroke, lower homocysteine, and even prevent insect bites.

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Foods that are bad for your immune system

So, are there foods that are bad for your immune system? Absolutely.

Your immune system is not just involved in fighting invaders like bacteria but also becomes activated when you eat foods to which you are intolerant or allergic. The most common allergenic foods include peanuts, shellfish, non-organic pasteurized cow's milk, commercial wheat, and soy.

Processed foods and foods produced with pesticides or not grown organically can also be problematic for your immune function.

Toxic metals such as cadmium, lead, and mercury are immunosuppressive. Some pesticides and preservatives can have a harmful impact on your gastrointestinal lining.

Food additives can also have harmful, damaging effects on the nutrient content of the food. For example, sulfites—a common additive to packaged foods—can destroy the vitamin B content in foods to which they have been added, rendering these foods less beneficial to your immune system.

To support and maintain a healthy immune system, you must provide support for the physical barriers in your body, especially your digestive tract. You must consume adequate protein and healthy fats, provide your body with micronutrients and phytonutrients that support healthy immune function, and decrease intake of allergens and toxins.

And you should also definitely go out of your way to explore foods that you might not currently be including, especially the eight scary, stinky foods you've discovered in this article.

Ben Greenfield

Ben Greenfield is an ex-bodybuilder, Ironman triathlete, obstacle course racer, human performance consultant, speaker and author of 13 books, including the New York Times Bestseller Beyond Training: Mastering Endurance, Health and Life. In 2008, Ben was voted as NSCA’s Personal Trainer of the year and in 2013 and 2014 was named by Greatist as one of the top 100 Most Influential People In Health And Fitness. Ben blogs and podcasts at BenGreenfieldFitness.com, and resides in Spokane, WA with his wife and twin boys.